Described in U.S. Pat. Nos. 4,910,943, 4,663,917, 439,108, 3,850,780, 4,128,985, 4,288,965, 442,385, 5,551,206, 5,125,217, 5,366,130, 5,463,850, 5,537,798, 5,622,033 and European Patents 0275181 and 0165819 are various packaging machines. In essence each of the packaging machines receives a strip of plastic film which is pulled passed a former so as to form a tube. The edges of the strip are sealed together and product delivered to the interior of the tube through the former. A sealing head engages the tube and forms the discrete bags which are then severed from the remainder of the tube. Typically closing bars and/or stripping bars may be employed to aid the packaging process.
The film can be pulled through the packaging machine by a variety of methods. For example the machine may be provided with a pair of co-operating belts, as described in a number of the above patent specifications, to which a vacuum may or may not be delivered. The film is drawn into contact with the driven belts to thereby pull the film through the machine. Alternatively, a pair of rollers may be provided. A vacuum is sometimes applied to the rollers to draw the film into frictional contact with the rollers. The rollers are driven so as to pull the film through the machine.
Some packaging machines are provided with vibration members which engage the sides of the tube and cause the sides of the tube to vibrate transverse of the longitudinal direction of movement of tube to cause the product being packaged to move towards the bottom of the package being formed. Some packaging machines are provided with discreet mechanisms which engage the side of the tube and cause the sides of the tube to vibrate transverse of the longitudinal direction of movement of tube to cause the product being packed to move towards the bottom of the package being formed in the same manner as the vibration members. This is to ensure that the product occupies a minimum volume and is not engaged by the closing bars and/or the sealing heads. This ensures proper sealing of the package.
Use of the above described vibration members can require intermittent movement of the plastic film. Initially, the plastic film is moved and product delivered to the interior thereof. The film is then held stationary while it is vibrated. The film is again moved and formation of the bag completed.
The above discussed previous method of applying vibration to the tubular bag material results in low production rates and unnecessarily increases forces in the machine as the machine is continually stopping and starting in respect of movement of the bag material.
Alternatively continuous motion machines are fitted with discreet mechanisms which rely on eccentric rotary or reciprocating mechanisms to impart the transverse vibration to the film tube. These additional devices add complexity and reliability issues to the packaging machine.